Mechanisms of furrow-applied biochar in enhancing rhizosphere soil microbiota and metabolites in continuous sesame cropping

Biochar application significantly reduces bacterial wilt and boosts yield in continuous sesame cropping, but high costs limit its widespread use. This study used metagenomic and metabolomic analyses to evaluate three biochar application strategies (surface [BR3, 15,000 kg ha⁻¹], furrow [BR4, 1,875 kg ha⁻¹], and no biochar [BR0]) across four sample types (D0/D1: diseased; H0/H1: healthy; rhizosphere/non-rhizosphere), analyzing their effects on microbial community as well as their functional and metabolic profiles in sesame soil. The results showed that BR4 significantly increased sesame yield by 26.57 % compared to the control (BR0). Biochar treatments (BR3/BR4) enhanced the relative abundance of Actinomycetota while suppressing Pseudomonas in rhizosphere and non-rhizosphere soils of diseased plants. Sphingobium amiense and S. indicum were differentially abundant in BR3H0 and BR4H0, respectively. We observed disruption of fatty acid metabolism in BR3D0, which was linked to growth inhibition in continuously cropped sesame. BR4H0 treatment significantly increased the relative abundance of pyruvate dehydrogenase and the superpathway for de novo biosynthesis of pyrimidine ribonucleotides. The rhizospheres treated with BR4 from healthy plants showed higher levels of C17-sphinganine (+2.79 percentage points) and 6-[3-(dihydroxyphenyl-methyl)-methoxybutyl]-benzodioxole (+0.18 percentage points) compared to diseased plants. Partial Least Squares Discriminant Analysis (PLS-DA) identified Jasmine lactone and Tris(hydroxymethyl)aminomethane as key metabolite discriminators under positive ion mode, as opposed to Taurochenoxycholate and Palmitic acid under negative ion mode. These findings suggest that furrow-applied biochar at a reduced rate (1,875 kg ha⁻¹) can enhance soil microbial structure, function, and metabolite composition, ultimately improving yield in continuous sesame cropping systems.